Here's my plan:
We look at it like an RTS.

The dumbasses are all allied with us right now. So we say to them: "Dudes I got a depression help me out send me some gold and iron and wood."
We take all we can get, then we spend half of all our money building a shitton of barackses and airports and factories and shit, and then spend the rest of our money building as many units as we can.
In the meantime, we go to Eurasia and build a bunch of cheap, strategically placed outposts- if our builders get taken out along the way it's no big deal, because the individual outpost is not the point.

We send out our builders and perhaps a couple of low-level units from our outposts into enemy territory and aggro some scouts, then retreat back into our "allies" territory. We keep doing this until our allies and enemies get drawn into their own conflicts and they say "Dued help us America" to which we will be forced to reply "shit dawg sorry I still gots a depression." Russia against Europe, the middle east against the other middle east, China against Korea, etc.

This is where the magic happens. We wait until our allies are almost dead, then we send in all the bombers we built at the airports and bomb the fuck out of Russia, the middle east, and Korea while they're still off ass raping our allies. They'll all immediately send their troops back, but their forces will be weakened from the fighting and exposed while moving. We use our remaining bombers to take down the units' armor while our ground troops sweep in to finish them off.

Now, depending on our success in these battles we may have two options. Either way, we have to immediately finish off our enemies before they recover, or else they'll retreat to some corner of the map world and annoy us for the rest of the game century, although they don't pose a serious threat anymore. If wiping them out hasn't dropped our army size too significantly, or if we can rebuild our units fast enough, we now have the option of un-allying and wiping out the rest of Europe, the middle East, and the far East, since they've already had their defenses destroyed.
We also take out Mexico and Canada as a matter of course, but that doesn't really take much strategizing.

Bang swoop, we now control the three northern continents; fuck the southern hemisphere, their continent bonuses are nowhere near ours. The game is won.